Stripline circulator having inner conductive coating for reducing volume of cavity

ABSTRACT

The surface of a magnet which is disposed in opposed relation with respect to a line conductor vacuum-deposited upon a magnetic medium in a stripline circulator is rendered electrically conductive. The frequency characteristics of such a stripline circulator are considerably improved.

United States Patent [191 Miura et al.

[ Ju1y3,l973

[ STRIPLINE CIRCULATOR HAVING INNER [58] Field of Search 333/11, 24.], 24.2

CONDUCTIVE COATING FOR REDUCING VOLUME OF CAVITY [56] References Cited [75] Inventors: Taro Miura, Suginami-ku, Tokyo; UNITED STATES PATENTS Kiichi Nakamura; Tadashi 3,324,418 6/1967 Caswell 333/l.l Hashimoto, both of schikawafshiy 3,355,680 11/1967 Saitzman 8! al. 333/1 .1 Chiba a" of Japan 3,614,670 10/1971 Wilson 333/1.[

[73] Assignee: T.D.K. Electronics Company Ltd., Primary Examiner-Paul L. Gensler Tokyo, Japan Attorney-Milton .1. Wayne et a1. [22] Filed: June 16, 1971 ABSTRACT [2]] Appl' 153,527 The surface of a magnet which is disposed in opposed relation with respect to a line conductor vacuum- 0 Foreign Application priority Data deposited upon a magnetic medium in a stripline circu- J later is rendered electrically conductive; The freune 30, 1970 Japan 45/57577 quency characteristics of such a stripline circulator are 52 us. Cl. ass/1.1, 333/84 M [51] Int. Cl. HOlp 1/32 3 Claims, 4 Drawing Figures YOKE MAGNET CONDUCTIVE COATING YOKE\ 2 3 IO a FERRITE MAGNET 4 GROUND PAIENIHIm am I 3.143.912 am 1 nr 2 MAGNETJ 4 H '5 PAIENIEnm am 3.743.972

am 2 m2,

LOSS FIG. 2 [db] PRIOR ART A o s FREQUENCY 2] LOSS [db] FIG. 3

' FREQUENCY [GHZ] STRIPLINE CIRCULATOR HAVING INNER CONDUCTIVE COATING FOR REDUCING VOLUME OF CAVITY BACKGROUND OF THE INVENTION The present invention relates to a circulator which is one of the microwave circuit elements, and more particularly to a new and improved stripline circulator.

In the microwave circuit field, circulators are widely used in duplexers, separation networks, amplifiers, modulators and the like, and recently have come to be used in television transmission techniques. Furthermore, circulators are operated not only in the microwave region but also in the light wave region.

Various types of circulators have been developed and they are generally divided into two types, one being the waveguide circulators and the other, the coaxial circulators, the latter being also called the stripline circulators. The stripline circulators are widely used in various fields because of their unusual compactness in size, light weight and a broad operating band. In general, the construction of a typical stripline circulator is such that a line conductor having a Y-shaped or three branches or X-shaped branches is vacuum-deposited on the upper surface of a magnetic medium such as ferrite while a ground conductor is vacuum-deposited upon the undersurface thereof, the external magnetic field being applied perpendicularly to the stripline conductor. A substantial portion of the electromagnetic energy transmitted from the input terminal is stored within the magnetic medium, but a fraction of the energy is radiated into the space above the line conductor. Since this space is enclosed in a yoke, it constitutes electrically a cavity resonator so that its effective electrical volume is increased especially when the external magnetic field is applied by use of ceramic magnets such as barium-ferrite magnets having a high dielectric constant. As a consequence, the resonance frequency of this space or cavity is included in the operating frequency band of the stripline circulators. When the cavity resonates at a resonance frequency within the operating frequency band, the forward loss or insertion loss is increased while the backward loss is decreased, so that the overall frequency characteristics of the circulators are degraded or deteriorated. To overcome this problem, when the prior art stripline circulators must be operated over a wide frequency range, an electromagnetic energy absorbing medium is inserted into the cavity so as to prevent the resonance of the cavity. However, the insertion of such an absorbing medium inevitably results in the complicated arrangements of various elements within the cavity or space in the stripline circulator. Furthermore, the insertion loss increases.

Therefore the present invention obviates the problems encountered in the prior art stripline circulators and described above.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a stripline circulator of the type in which the surface of a magnet for applying the external magnetic field to a line conductor vertically is rendered electrically conductive.

According to one embodiment of the present invention, a pair of barium ferrite magnets are fixed to the opposing inner walls of an airtight yoke and a ferrite magnetic medium is interposed between them. A line conductor having three branches is vacuum-deposited upon the magnetic medium and a base conductor is also vacuum-deposited on the undersurface thereof. Three coaxial connectors are fixed through the wall of the yoke in alignment with the threebranches of the stripline respectively as the terminals. The surface of the magnet in opposed relation with the magnetic medium is rendered electrically conductive by nonelectrolytic plating or by applying an electrically conductive coating.

In the stripline circulator in accordance with the present invention, the volume of a space or cavity formed above the stripline conductor is reduced so that the resonance frequency of the cavity may be displaced beyond the operating frequency region of the circulator.

The present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. l-a is a sectional view of a stripline circulator in accordance with the present invention;

FIG. I-b is a sectional view taken along the line A-A' of FIG. 1-0; I

FIG. 2 is a graph illustrating the frequency characteristics of a prior art stripline circulator; and

FIG. 3 is a graph illustrating the frequency characteristics of the stripline circulator in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

Referring to FIG. 1, an airtight yoke 1 is provided with a second yoke 2, which is fixed to the upper surface of the airtight yoke l and carries at the undersurface thereof a magnet 3 held by a holding element. A second magnet 4 is directly fixed to the lower portion of the airtight yoke 1 in opposed relation with the upper or first magnet 3. These magnets 3 and 4 are generally made of ceramic-like barium ferrite having a high dielectric constant. A magnetic medium 5 is interposed between the upper and lower magnets 3 and 4, and is generally made of ferrite. A line conductor generally indicated by 10 consisting of a circular conductor 6 and three branched striplines 7, 8 and 9 is vacuum-deposited upon the magnetic medium 5. A ground or base conductor 11 is also vacuum-deposited on the undersurface of the magnetic medium 5. Three coaxial connectors 12, I3 and 14 extend through the side wall of the airtight yoke I in alignment with the three striplines 7, 8 and 9 respectively. These three coaxial connectors 12, 13 and 14 serve as the terminals of the striplines 7, 8 and 9, and a grounding conductor 15 is interposed between the lower magnet 4 and the yoke I.

Theoretically, in the stripline circulator of the type illustrated in FIG. 1, the electromagnetic energy is for example transmitted from the terminal 12 into the stripline circulator and is derived from the terminal 13 without any reflection and attenuation, and no electromagnetic energy leaks from the terminal 14. Similarly the electromagnetic energy transmitted from the terminal I3 is transmitted only to the terminal 14 without any attenuation and leakage. However, in practice there are some reflection, attenuation and leakage.

A fraction of the electromagnetic energy entered from the terminal 12 is radiated into the space above the line conductor 10, and since this space is enclosed by the yokes 1 and 2, it constitutes a cavity resonator electrically. Since the magnets 3 and 4 are generally of a barium ferrite having a high dielectric constant, an effective electrical volume of the cavity including the magnet 3 is increased so that when thecirculator is operated over a wide band, there is a case in which a-resonant frequency of this cavity is included in said wide band. When the cavity resonates at a frequency within the wide band at which the circulator is operated, the forward loss of the circulator is increased while the backward loss is reduced, so that the frequency characteristics of the circulator are deteriorated or degraded.

Referring to FIG. 2 illustrating the examples of the frequency characteristic curves of the prior art stripline circulator, the curves were obtained when the diameter of the magnetic medium 5 was mm, the thickness of the ferrite was 1.7 mm and the magnetic field applied across the magnets 3 and 4 was 950 Oe (oersteds). The curve indicated by A in FIG. 2 shows the forward loss while the curve indicated by B, the backward loss. It is seen that the influence due to the resonance of the cavity occurs in the frequency range between 7.0 and 8.0 GHz.

It is of course understood that when the resonant frequency of the cavity is so increased as to be displaced out of the operating frequency band of the circulator, the circulator will be free from the influence of the resonant frequency of the cavity. For this purpose, the present invention contemplates rendering the surface of the circulator magnet 3 conductive by nonelectrolytic plating or applying an electrically conductive coating. Therefore, the volume of the cavity may be reduced without adversely affecting the magnetic circuit so that the resonant frequency of the cavity may be increased so as to be out of the operating frequency band of the circulator. As a consequence, the deterioration or degradation of the frequency characteristics of the circulator may be effectively prevented, and the circulators capable of operating over a wide frequency band may be provided. According to the present invention, the reflection of the electromagnetic energy is made on the metallic surface of the magnet 3 so as to displace the resonance frequency of the cavity out of the operating frequency band of the circulator, so that the insertion loss will not be increased.

The characteristic curves illustrated in FIG. 3 were obtained under the same conditions used to obtain the characteristic curves shown in FIG. 2, except that the surface of the magnet 3 was rendered conductive in accordance with the present invention. The curve A indicates the forward loss while the curve B, the backward loss. It is seen that when the surface of the magnet on the side of the line conductor in the stripline circulator is rendered electrically conductive in accordance with the present invention, the frequency characteristics both in the forward and backward directions may be much improved.

What is claimed is:

1. A stripline circulator comprising an airtight yoke, a pair of spaced-apart upper and lower ferrite magnets having downwardly and upwardly facing surfaces respectively, said magnets being located within said yoke, a ferrite magnetic medium having upper and lower surfaces interposed between said pair of spaced-apart magnets, a line conductor having upper and lower surfaces, said lower surface of said line conductor touching said upper surface of said magnetic medium, cavity resonator means formed between the upper surface of said line conductor and the downwardly facing surface of said upper magnet, a ground conductor sandwiched between said lower surface of said magnetic medium and the upwardly facing surface of said lower magnet, and an electrically conductive medium placed on the downwardly facing surface of said upper magnet for reducing the volume of said cavity resonator.

2. A stripline circulator as set forth in claim 1 wherein said pair of magnets comprises ceramic magnets having a high dielectric constant.

3. A stripline circulator as set forth in claim 1; wherein said line conductor and said ground conductor are vacuum deposited on said upper and lower ferrite surfaces, respectively. 

2. A stripline circulator as set forth in claim 1 wherein said pair of magnets comprises ceramic magnets having a high dielectric constant.
 3. A stripline circulator as set forth in claim 1; wherein said line conductor and said ground conductor are vacuum deposited on said upper and lower ferrite surfaces, respectively. 